The prior art has known various locking devices. U.S. Pat. No. 1,806,694 discloses an eccentrically mounted washer held by a screw and movable into a notch on a punch to hold the punch in place. U.S. Pat. No. 1,003,369 discloses a chuck wherein a square, toothed gripping device rotates slightly to grip the periphery of the head of a bolt. U.S. Pat. No. 1,899,326 discloses a rotatable lock member with an enlarged head carrying a helical cam surface to enter a slot in a tool and force it axially. U.S. Pat. No. 4,597,699 discloses a rotatable eccentric cam locking member which can engage either axial side of a conical button coaxially on the tool.
It is desired to achieve a quick-change mechanism to permit fast changing of tools on small size multi-spindle machines. Most of these machines have limited space in their tooling area, so that any quick-change device that could be accommodated has to be very compact. The structure disclosed in U.S. Pat. No. 4,597,699 is relatively complex and too large for these small size machine tools. The structure shown in U.S. Pat. No. 1,003,369 cannot maintain the bolt coaxial with the chuck, and would only be useful for the relatively imprecise positioning required in threading a bolt into a nut. Further, it does not lock the bolt axially into the chuck. The structure disclosed in U.S. Pat. No. 1,806,694 is not a quick-change device because it would require the use of two screwdrivers or like implements, one to pry the eccentric washer into or out of engagement with the notch, and the other screwdriver to tighten or loosen the bolt 19. The structure disclosed in U.S. Pat. No. 1,899,326 requires a specially machined locking device with a helical cam surface machined on it, plus an arcuate notch in the head in a position to receive the tool. Also, a specially machined notch must be provided in the tool with a corresponding helical surface therein.